The present invention relates to a battery charging system. More particularly, the present invention relates to a clamp circuit that stabilizes a battery charging system when a battery cell is detected as being decoupled from the system.
Rechargeable lithium based batteries, including Lithium-Ion batteries and Lithium-Polymer batteries, are used in portable applications such as cellular telephones. A Lithium battery is gradually charged by an external power supply. The Lithium battery is initially charged via a trickle current path to a low threshold voltage. The Lithium battery is then charged via a regular current path to a high threshold voltage.
The present invention discloses a clamp circuit that stabilizes a battery charging system when a battery is detected as being decoupled from the system and a power supply is providing current to the system. A battery detect circuit detects when the battery is decoupled from the system. A biasing circuit provides a biasing current to the clamp circuit when the battery is detected as being decoupled from the system. The clamp circuit shunts current from a battery charge terminal to maintain a stable condition in the battery charging system such that the system can withstand constant charge from the power supply without becoming damaged. The clamp circuit is deactivated when the battery is coupled to the system. The battery detect circuit includes a power management circuit that limits the power dissipated by the system.
In one example, the present invention is related to an apparatus for stabilizing a battery charging circuit when a battery is detected as being decoupled from the apparatus. The apparatus comprises a battery detect circuit and a clamp circuit. The battery detect circuit is arranged to detect when the battery is decoupled from the apparatus. The clamp circuit is coupled to a battery charge terminal of the apparatus. The clamp circuit is arranged to maintain a stable condition in the apparatus by shunting current from the battery charge terminal when the battery is detected as being decoupled from the apparatus.
In another example, the present invention is related to an apparatus for stabilizing a battery charging circuit when a battery is detected as being decoupled from the apparatus. The apparatus comprises a primary charge path circuit, a secondary charge path circuit, a battery detect circuit, and a clamp circuit. The primary charge path circuit is arranged to selectively couple power from a power supply to the battery when the voltage associated with the battery is above a threshold, such that the battery is selectively charged by a primary charging current. The secondary charge path circuit is arranged to couple power from the power supply to the battery when the voltage associated with the battery is below the threshold, such that the battery is selectively charged by a secondary charging current. The battery detect circuit is arranged to detect when the battery is decoupled from the apparatus. The clamp circuit is arranged to maintain the secondary charging current when the battery is detected as being decoupled from the apparatus, such that a stable condition in the apparatus is maintained.
In still another example, the present invention is related to a method of stabilizing a battery charging circuit when a battery is detected as being decoupled from a battery charge terminal. The method comprises detecting when the battery is decoupled from the battery charge terminal and shunting current from the battery charge terminal to maintain a stable condition in the battery charging circuit.
In still yet another example, the present invention is related to an apparatus for stabilizing a battery charging circuit when a battery is detected as being decoupled from a battery charge terminal. The apparatus comprises a means for detecting when the battery is decoupled from the battery charge terminal and a means for shunting current from the battery charge terminal to maintain a stable condition in the battery charging circuit.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawing, which is briefly summarized below, to the following detailed description of illustrative embodiments of the invention, and to the appended claims.